May I take a try?
I believe there is a God, first of all. I have a feeling that you grant His existence only for the sake of argument. I may be wrong about that. I don't know.
If you do believe in God, isn't it sort of foolish to judge his actions by our standards?
I'm reminded of the story of Sodom and Gommorah. Yes, God did destroy the cities, but only after multiple warnings of what He expected of the citizens of those cities.
It wasn't an unprovoked leveling of two towns without a reason.
When Jesus cleared out the temple of the money changers, He wasn't doing it just to raise hell, so to speak, but because he expected certain forms of behavior. What many would call right behavior.
Can you name any such occurances in the Bible where violence on the part of God is gratuitous?
I expect you may cite some examples. Great. But again, if you grant the existance of God, how do we know with certainty that those examples are in fact gratuitous? How, if this is your decision, did you get to know God's mind?
By denying God you also create another problem. You are in effect makin g man God. It must be man, using his powers, to determine what is right and what is wrong, and why that is. I'm forced to again point to the failed socialist systems, especially the failed atheist socialist systems. If Man is God, if man creates the rules, isn't it only reasonable to expect him to behave like a Roman Emperor, or an Asian potentate?
I have no desire to convert you, but only to try to answer your question. Maybe Stu can do a better job than me. To me the important point is that there is an ultimate authority. That authority is what provides our moral compass.
PS, War, under the correct conditions is sanctioned by such people as St. Augustine and St. Thomas Aquinas, but those sanctions don't include an appetite for a steak dinner.